Typically to install a window pane in a wooden/plastic/metal frame, the glass pane is firstly held in position against nails or other clasps and then fixed into position by putty or plasters material. Conventional putty is a cement made from whiting and linseed oil which hardens over time to provide a peripheral rim of the window pane, thus separating interior and exterior environments and preventing air, moisture and/or heat transfer. The installation is completed once the putty has dried and this usually takes up to 6 hours or so depending on the kind of plasters used.
To remove a window pane after it has been fixed in position in a frame requires the window itself to be shattered so that the hardened putty or plasters can be scraped/chiselled away from the fame. The removal operation can cause damage to the frame and varnishes.
In use, the window pane is held rigidly around its edges so that even relatively small vibrational mechanical movements such as with earthquakes or bomb blasts or strong winds can cause the window pane to shatter.
In the automotive industry, cars direct from the factory production line typically have the windscreens and other fixed windows, including light assemblies fixed into position by placing the glass against a frame rim and using adhesives so as to direct glaze the glass. The life span of a windscreen and other fixed windows are significantly shorter than that of the vehicle itself partially due to degradation or damage or being deliberately broken by vandals/car thieves. Thus a motorist may need to replace the windscreen several times during the vehicle's lifetime.
Additionally, glued glazings have to be replaced any time the window, especially the windscreen, has been damaged in its optical performance by, for example, impact stones or other fractures or abrasion by wipers. Damage to the window surface can increase the scattering of light and may reduce the visibility to levels below safety limits. Moreover, regulations of motor worthiness (MOT) stipulate that there can be no chips or visual impairments on laminated windscreens, so whereas recent improvements have made the windscreens shatter-proof, they are still prone to chipping and fracturing and thus will require replacement.
The process of replacing vehicle windscreens is both laborious and time consuming. The automotive glass fitter has first to remove the defective windscreen (usually in intact form), however the windscreen is firmly bonded in place and the adhesive sealant is hardened. Typically the fitter uses a device comprising a cheesewire. The cheesewire is used to cut/saw through the hardened rubber along the periphery of the windscreen. This process requires physical force and can lead to musculo-skeletal conditions in the fitters themselves as a result of repetitive strain injury. Further problems associated with this method are that the cheesewires can overheat due to friction, additionally the wires themselves can break.
Other methods of detaching the windscreen from the adhesive sealant include: the use of mechanical oscillator knives/cutters to cut through the hardened material or; directed heat such as a laser beam to soften the sealant prior to removing the windscreen with either cheesewire or specialised bladed tools. The problem with a method where heat is directly applied to the sealant is that the heat required to soften the hardened adhesive sealant can concomitantly and inadvertently damage the vehicle's paintwork and/or other exterior surfaces. For example, a pulsed laser that is set to pulse too fast will not generate enough energy to char the adhesive sealant and a pulsed laser that is set too slow will bum the adhesive sealant and liquify it.
Once the windscreen has been freed from the rubber sealant it can be removed and the surround scraped before it is replaced. It is known from the prior art to use urethane based adhesives to fix/seal the replaced windscreen in place and to apply the adhesive from a dispenser gun to specific peripheral edges so as not to impinge on the viewing capacity of the windscreen. The adhesive typically takes about 8 hours to cure.
Recent advances to the industry have provided for the inclusion of fast cure agents/catalysts so as to speed up the time from vehicle drop-off to vehicle collection. The fast cure agents/catalysts can be provided pre-mixed in the adhesive composition or alternatively can be mixed with the adhesive at the point of exit from a dispensing gun. However the problem still remains that the removal of a defective windscreen and its subsequent replacement is a laborious and time consuming process which can result in damage to the dashboard interior or vehicle paint-work.
An adhesive that could satisfy vehicle safety crush and crash standards and provide for easy, effective and damage-proof removal of a defective windscreen or other fixed glazing from a vehicle would offer immediate improvement to the industry and consumer.
In a completely different technical field it is known to provide thermoexpandable microcapsules or microspheres for use in the manufacture of porous or lightweight materials with density (weight) reduction, acoustic and thermal insulating properties as covering materials or walls. The microcapsules or microcapsules comprises a polymer shell or shell of some other similar material, the shell being of certain thickness and chemical/physical/mechanical properties. The shell encapsulates materials such as volatile organic solvents, expandable gases or activating agents, including explosives or any other such material which is capable of exploding the shell and expanding at certain specified conditions with a selected matrix. The microcapsules, when heated to a sufficient temperature, typically in the region of about 75-180° C., depending on the encapsulated substance and the shell composition and thickness, can produce an increase of their volume at high expansion rate in some instances at a volumetric expansion limit of up to 70 to 160 times the original volume. The percentage and distribution of the microspheres in a given composition, their expansion ratio, the temperature operating range, the softening transition range of the shell material and the matrix cohesion and consistency are all parameters which are able to influence the expansion volume of a layer between two materials.
We have discovered that by mixing an appropriate adhesive in a suitably rheological performance with a certain % in powdered form of specially developed microcapsules having a specific range of size distribution, the resulting composition is effective at providing glazing adhesion and sealing. Moreover, of particular advantage is that the adhesive bonds in the composition can be weakened by the application of direct heat to the composition thereby allowing sufficient softening of the adhesive material so that a vehicle windscreen/fixed glazing can be easily lifted up and so rapidly removed. The lifting pressure can be predicted by a computational software which is part of this invention and treats the expanding microspheres like a spring mechanical pressure actuator in the volume of the adhesive state and like a “bombing” actuator at interfaces between two layers.
We believe that the invention provides the first application/use of a polyester material in the automotive glazing industry.
It will be appreciated that the adhesive of the invention has application in other areas especially where two surfaces are to be bonded together and where one surface may subsequently need replacing following damage or ware, for example, and without limitation; shower doors and vehicle panels and other building glazing applications.
Reference herein to vehicle is intended to include, without limitation car, lorry, van ship, boat, plane, cable car, helicopter, hovercraft and any other form of transport in which there is fixed glazing.